1. Field of the Invention
The invention relates to developing apparatuses which develop latent electrostatic images for various recording apparatuses such as xerographic copying machines and laser printers. More particularly, it is directed to a developing apparatus which develops latent electrostatic images using a developing agent consisting of a single magnetic component.
2. Related Art
FIGS. 8 and 9 show a developing apparatus of such type as using a single-component developing agent consisting solely of magnetic toner. Specifically, such a developing apparatus includes: a plurality of magnets fixed within a rotatable cylindrical sleeve; a developing agent carrying body b which rotates while attracting a developing agent, or toner T, on the sleeve (hereinafter referred to as "developing roll"); a blade c which forms the toner T into a thin layer by being in pressure contact with the developing roll b, and frictionally charges the toner T; a toner stirring chamber e disposed along the length of the developing roll b (hereinafter referred to as "stirring chamber"); and a toner delivering/feeding member f disposed in parallel to the developing roll b within the stirring chamber e.
In the developing apparatus thus constructed., the toner T is delivered from the stirring chamber e to a developing region facing a latent electrostatic image carrying body d by being attracted by the developing roll b so that a latent electrostatic image will be developed into a permanent image. Part of the toner T which has not contributed to the development is delivered back into the developing apparatus in association with rotation of the developing roll b, separated from the developing roll b, and returned to the stirring chamber e.
The developing apparatus thus constructed replenishes the toner T to the stirring chamber e as shown in FIG. 9. That is, after being dropped into an end of the stirring chamber e from a toner box a located at an upper position of the developing apparatus, the toner T is delivered to the other end of the stirring chamber e by the toner delivering/feeding member f and uniformly distributed over the stirring chamber e.
In delivering the toner from one end to the other of the stirring chamber, the toner is distributed uniformly over the stirring chamber by repeating the development cycle described above. In other words, the toner delivered to the stirring chamber advances toward the opposite end of the stirring chamber while moving from the stirring chamber to the developing region and back to the stirring chamber.
However, such an arrangement results in the following inconveniences. Since the toner is rubbed on the blade many times as it advances along the stirring chamber, part of the toner which is at the back in the toner delivery direction is excessively loaded compared with the toner which is in the front, and this causes an additive (such as silica) which is externally added to the toner to adjust charging amounts is blended into the toner or separated from the toner. As a result, the excessively loaded toner is deposited heavily at the back of the stirring chamber, charging such toner less intensely than that in the front. This causes the problem of reducing the densities in part of a recording image developed with such toner.
It should be noted that this problem is not unique to developing apparatuses of such type that toner is pressed and subjected to frictional charging using a blade. For example, as shown in FIG. 10, even in a developing apparatus of such type that toner T which has been frictionally charged by stirring is formed into a layer of a predetermined thickness by a noncontact type trimming member g, the toner T is likewise loaded at stirring or at toner layer forming, thereby suffering from the same problem.